Methods for codebook sub-sampling
Disclosed are methods for codebook sub-sampling. In various implementations, a wireless terminal receives a reference signal, determines, based on the reference signal, a first precoding index i 2 for a first subband and a second precoding index i′ 2 for a second subband. The wireless terminal transmits a representation of i 2 and a representation of i′ 2 to a base station. In various implementations, i′ 2 belongs to the set S i 2 which, in one implementation, equals {mod(i 2 −K 1 +k,K), k=0, 1, . . . , K 2 }, where K 1 >1, and where K 2 >1 and K>1 are integers. According to an implementation, the wireless terminal receives the reference signal from a first base station and transmits the representations of i 2 and i′ 2 to a second base station.
1. A method in a wireless terminal, the method comprising:
receiving a reference signal from a first base station;
determining a first precoding index i 1 corresponding to a first precoding matrix based on the reference signal, wherein i 1 is an index of a first codebook;
determining a derived precoding index I PMI =mod(i 1 ,K), wherein K>1 is an integer; and
transmitting a representation of I PMI to a second base station.
2. The method of claim 1 further comprising:
determining a second precoding index i 2 based on the reference signal, wherein the second precoding index i 2 is an index of a second codebook, and wherein the first precoding index and the second precoding index jointly determine a precoding matrix with a product structure.
3. The method of claim 1 further comprising:
transmitting a channel quality indication to the second base station, wherein the channel quality indication information refers to one or more spatial layers, and wherein the channel quality indication is conditioned on I PMI .
4. The method of claim 1 wherein transmitting the representation of I PMI to the second base station comprises:
transmitting a first channel-state information report including a representation of i 1 in a first uplink subframe to the second base station; and
transmitting a second channel-state information report including at least a representation of i 2 in a second uplink subframe to the second base station.
5. The method of claim 4 wherein the first and second channel-state information reports are transmitted with different periodicities.
6. The method of claim 1 wherein transmitting the representation of I PMI to the second base station comprises transmitting the representation of I PMI to the second base station over a physical uplink control channel or a physical uplink shared channel.
7. A wireless terminal comprising:
at least one transceiver operative to receive a reference signal from a first base station;
a controller, operatively coupled to the at least one transceiver operative to:
determine a first precoding index i 1 corresponding to a first precoding matrix based on the reference signal, wherein i 1 is an index of a first codebook; and
determine a derived precoding index I PMI =mod(i 1 ,K), wherein K>1 is an integer; and
at least one transceiver operative to transmit a representation of I PMI to a second base station.
8. The wireless terminal of claim 7 wherein the controller is further operative to:
determine a second precoding index i 2 based on the reference signal, wherein the second precoding index i 2 is an index of a second codebook, and wherein the first precoding index and the second precoding index jointly determine a precoding matrix with a product structure.
9. The wireless terminal of claim 7 further comprising the controller operative to cause one of the at least one of the transceivers to transmit:
a channel quality indication to the second base station, wherein the channel quality indication information refers to one or more spatial layers, and wherein the channel quality indication is conditioned on I PMI .
10. The wireless terminal of claim 7 wherein transmitting the representation of I PMI to the second base station comprises:
transmitting a first channel-state information report including a representation of i 1 in a first uplink subframe to the second base station; and
transmitting a second channel-state information report including at least a representation of i 2 in a second uplink subframe to the second base station.
11. The wireless terminal of claim 10 wherein the first and second channel-state information reports are transmitted with different periodicities.
12. The wireless terminal of claim 7 wherein transmitting the representation of I PMI to the second base station comprises transmitting the representation of I PMI to the second base station over a physical uplink control channel or a physical uplink shared channel.